Thick-wire bonding, which is also referred to as ribbon bonding, represents a widely used connecting technique, in particular in power electronics. This known connecting technique is used to produce electrical connections between conductor tracks, terminal lugs and component contacts by corresponding bridging by means of wires or ribbons. The connection of the wire to the bonding buffer at the corresponding contact area is produced by static contact pressure and a high-frequency oscillation of a clamping tool, whereby the wire enters into a solid and integral material bond with the contact area in a form of friction welding process. Mainly aluminium and copper wires are used most frequently for the known connecting techniques. Aluminium bonding wires have the advantage over copper bonding wires that they are more ductile and less hard. These known friction welded connections with aluminium wires are generally easy to produce, mainly as a result of an inherently thin layer of aluminium oxide surrounding the wire. This oxide layer adheres firmly to the wire and thereby provides solid support for the required friction during the friction welding process, on the one hand by abrasion of the part to be joined and on the other hand by exposing metallically pure aluminium. Metals, preferably copper, aluminium or metallic coatings, for example in the form of nickel-gold, nickel or else palladium, can be considered as a joining partner.
WO 2013/053420 A1 discloses a power semiconductor chip with metallic molded bodies for connecting thick wires or ribbons and a method for the production thereof. It focuses especially on thick-wire copper bonding technology, for achieving improved load cycle endurance. The known power semiconductor chip has on its upper side potential surfaces on which a metal molded body is fixed in an electrically and thermally well conducting manner. Such a metal molded body is fastened onto a metallization layer of the semiconductor with the aid of a connecting layer by low-temperature sintering technology or else by way of diffusion soldering or adhesive bonding.
WO 2013/053419 A1 describes a method for providing a connection between metal molded bodies and a power semiconductor chip for the connection thereof by thick wires or ribbons. The basic structure of the known power semiconductor chip that is also described there corresponds to that previously mentioned, the production of the metal molded bodies by means of an organic carrier film being addressed especially by this prior art.
Furthermore, DE 20 2012 004 434 U1 likewise describes a metal molded body for providing a connection of a power semiconductor chip with potential surfaces on the upper side to thick wires. This known connecting technology is likewise aimed at copper thick-wire bonding.
All the known methods share the common feature that the connecting of the thick wires or ribbons takes place on a surface of the metal molded body that is substantially smooth, at most has a roughness that is caused during production. While aluminium wires have a solidly bonding oxide layer, copper wires, though they form an oxide, cannot serve as the required means of abrasion during thick-wire bonding because the oxide does not solidly bond. In addition, copper is a harder material than aluminium. On the other hand, copper is a material with a significantly higher thermal conductivity and lower electrical resistance than aluminium, and is therefore to be given priority when choosing the material for the contact wires. In order that a sufficiently good material bond with the metal molded body can be achieved during the wire bonding, i.e. by way of the contact area of the said body, usually the static pressure and the energy input in the ultrasonic welding for the wire bonding are increased significantly. However, this entails the risk of damage to the semiconductor structures being connected to. Especially whenever the contact area on the metal molded body consists of a non-ductile, non-oxidized material, this can give rise to problems in producing a secure bond by means of a thick copper wire with regard to a connection that is reliable under a relatively high number of load cycles.